The present invention generally relates to a disk holder for holding a rotating disk against a surface and more particularly, relates to a conformal disk holder for holding a CMP pad conditioning disk against the surface of a polishing pad for conducting a CMP pad conditioning process.
Apparatus for polishing thin, flat semi-conductor wafers is well known in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semi-conductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head; a wafer unload station; or, a wafer load station.
More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is xe2x80x9cplanarizedxe2x80x9d or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
A perspective view of a typical CMP apparatus is shown in FIG. 1A. The CMP apparatus 10 consists of a controlled mini-environment 12 and a control panel section 14. In the controlled mini-environment 12, typically four spindles 16, 18, 20, and 22 are provided (the fourth spindle 22 is not shown in FIG. 1a) which are mounted on a cross-head 24. On the bottom of each spindle, for instance, under the spindle 16, a polishing head 26 is mounted and rotated by a motor (not shown). A substrate such as a wafer is mounted on the polishing head 26 with the surface to be polished mounted in a face-down position (not shown). During a polishing operation, the polishing head 26 is moved longitudinally along the spindle 16 in a linear motion across the surface of a polishing pad 28. As shown in FIG. 1A, the polishing pad 28 is mounted on a polishing disc 30 rotated by a motor (not shown) in a direction opposite to the rotational direction of the polishing head 26.
Also shown in FIG. 1a is a conditioner arm 32 which is equipped with a rotating conditioner disc 34. The conditioner arm 332 pivots on its base 36 for conditioning the polishing pad 38 for the in-situ conditioning of the pad during polishing. While three stations each equipped with a polishing pad 28, 38 and 40 are shown, the fourth station is a head clean load/unload (HCLU) station utilized for the loading and unloading of wafers into and out of the polishing head. After a wafer is mounted into a polishing head in the fourth head cleaning load/unload station, the cross head 24 rotates 90xc2x0 clockwise to move the wafer just loaded into a polishing position, i.e., over the polishing pad 28. Simultaneously, a polished wafer mounted on spindle 20 is moved into the head clean load/unload station for unloading.
A cross-sectional view of a polishing station 42 is shown in FIGS. 1B and 1C. As shown in FIG. 1B, a rotating polishing head 26 which holds a wafer 44 is pressed onto an oppositely rotating polishing pad 28 mounted on a polishing disc 30 by adhesive means. The polishing pad 28 is pressed against the wafer surface 46 at a predetermined pressure. During polishing, a slurry 48 is dispensed in droplets onto the surface of the polishing pad 28 to effectuate the chemical mechanical removal of materials from the wafer surface 46.
An enlarged cross-sectional representation of the polishing action which results form a combination of chemical and mechanical effects is shown in FIG. 1C. The CMP method can be used to provide a planner surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An outer layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing, a metal oxide layer can be formed and removed repeatedly.
During a CMP process, a large volume of a slurry composition is dispensed. The slurry composition and the pressure applied between the wafer surface and the polishing pad determine the rate of polishing or material removal from the wafer surface. The chemistry of the slurry composition plays an important role in the polishing rate of the CMP process. For instance, when polishing oxide films, the rate of removal is twice as fast in a slurry that has a pH of 11 than with a slurry that has a pH of 7. The hardness of the polishing particles contained in the slurry composition should be about the same as the hardness of the film to be removed to avoid damaging the film. A slurry composition typically consists of an abrasive component, i.e, hard particles and components that chemically react with the surface of the substrate. For instance, a typical oxide polishing slurry composition consists of a colloidal suspension of oxide particles with an average size of 30 nm suspended in an alkali solution at a pH larger than 10. A polishing rate of about 120 nm/min can be achieved by using this slurry composition. Other abrasive components such as ceria suspensions may also be used for glass polishing where large amounts of silicon oxide must be removed. Ceria suspensions act as both the mechanical and the chemical agent in the slurry for achieving high polishing rates, i.e, larger than 500 nm/min. While ceria particles in the slurry composition remove silicon oxide at a higher rate than do silica, silica is still preferred because smoother surfaces can be produced. Other abrasive components, such as alumina (Al3O2) may also be used in the slurry composition.
The polishing pad 28 is a consumable item used in a semiconductor wafer fabrication process. Under normal wafer fabrication conditions, the polishing pad is replaced after about 12 hours of usage. Polishing pads may be hard, incompressible pads or soft pads. For oxide polishing, hard and stiffer pads are generally used to achieve planarity. Softer pads are generally used in other polishing processes to achieve improved uniformity and smooth surface. The hard pads and the soft pads may also be combined in an arrangement of stacked pads for customized applications.
A problem frequently encountered in the use of polishing pads in oxide planarization is the rapid deterioration in oxide polishing rates with successive wafers. The cause for the deterioration is known as xe2x80x9cpad glazingxe2x80x9d wherein the surface of a polishing pad becomes smooth such that the pad no longer holds slurry in-between the fibers. This is a physical phenomenon on the pad surface not caused by any chemical reactions between the pad and the slurry.
To remedy the pad glazing effect, numerous techniques of pad conditioning or scrubbing have been proposed to regenerate and restore the pad surface and thereby, restoring the polishing rates of the pad. The pad conditioning techniques include the use of silicon carbide particles, diamond emery paper, blade or knife for scrapping the polishing pad surface. The goal of the conditioning process is to remove polishing debris from the pad surface, re-open the pores, and thus forms micro-scratches in the surface of the pad for improved life time. The pad conditioning process can be carried out either during a polishing process, i.e. known as concurrent conditioning, or after a polishing process.
While the pad conditioning process improves the consistency and lifetime of a polishing pad, a conventional conditioning disk is frequently not effective in conditioning a pad surface after repeated usage. A conventional conditioning disk for use in pad conditioning is shown in FIGS. 2A and 2B.
Referring now to FIG. 2A, wherein a perspective view of a CMP publishing station 42 is shown. The polishing station 42 consists of a conditioning head 52, a polishing pad 28, and a slurry delivery arm 54 positioned over the polishing pad. The conditioning head 52 is mounted on a conditioning arm 58 which is extended over the top of the polishing pad 28 for making sweeping motion across the entire surface of the pad. The slurry delivery arm 54 is equipped with slurry dispensing nozzles 62 which are used for dispensing a slurry solution on the top surface 60 of the polishing pad 56. Surface grooves 64 are further provided in the top surface 60 to facilitate even distribution of the slurry solution and to help entrapping undesirable particles that are generated by coagulated slurry solution or any other foreign particles which have fallen on top of the polishing pad during a polishing process. The surface grooves 64 while serving an important function of distributing the slurry also presents a processing problem when the pad surface 60 gradually worn out after successive use.
The conditioning disk 68, shown in FIG. 2B is formed by embedding or encapsulating diamond particles 50 in nickel 56 coated on the surface 70 of a rigid substrate 22. FIG. 2B is a cross-sectional view of a new conditioning disk with all the diamond particles 32 embedded in nickel 34. In the fabrication of the diamond particle conditioning disk 68, a nickel encapsulant 56 is first mixed with a diamond grit which includes diamond particles 50 and then applied to the rigid substrate 22.
The conditioning disk 68 is mounted onto a disk holder, as shown in FIGS. 3A-3C, which is constructed by three structural members, i.e. a cross member 74, a ring member 78 and a holder member 80. The conventional disk holder that is constructed by the three members 74,78 and 80 requires a complicated assembling process when the parts are taken apart during a preventive maintenance procedure. For instance, the three members shown in FIGS. 3A-3C, are held together by a total of sixteen screws and therefore, require as long as two hours for completing a preventive maintenance procedure. Moreover, the original design utilizes the cross member 74 as a flexural member for providing conformability of the conditioning disk to a surface of a polishing pad. The cross member does not have a rigid structure and is prone to various mechanical damages when not used or installed properly. Breakage or fracture of the cross member 74 is frequently encountered which results in substantial down time of the conditioning disk, increased rework rate and reduced yield.
It is therefore an object of the present invention to provide a disk holder for holding a rotating disk against a surface that does not have the drawbacks or shortcomings of the conventional disk holder supplied by the machine manufacturer.
It is another object of the present invention to provide a conformal disk holder for holding a rotating disk intimately against a polishing pad surface.
It is a further object of the present invention to provide a conformal disk holder for holding a CMP pad conditioning disk against a polishing pad surface.
It is another further object of the present invention to provide a conformal disk holder for holding a rotating disk against a surface wherein the disk holder is allowed at least a 5xc2x0 tilt from a horizontal plane in order to conform to the surface that is being conditioned.
It is still another object of the present invention to provide a conformal disk holder for holding a rotating disk against a surface to be conditioned wherein the disk holder allows a tilt between about 5xc2x0 and about 30xc2x0 from a horizontal plane.
It is yet another object of the present invention to provide a conformal disk holder for holding a CMP pad conditioning disk against a polishing pad surface which is effective in following a profile of the polishing pad surface for activating fibers on the pad.
In accordance with the present invention, a conformal disk holder for holding a rotating disk against a surface to be conditioned is provided.
In a preferred embodiment, a conformal disk holder for holding a rotating disk against a surface to be conditioned can be provided which includes a holder body of circular shape that has a first diameter, a center aperture for accessing a center flexural plate, and a means for connecting to a rotating shaft; a center flexural plate of circular shape that has a second diameter smaller than the first diameter for fitting inside a downwardly protruded edge portion on the holder cover; the center flexural plate is equipped with a center protrusion that has a downwardly facing convex surface and at least three notch openings equally spaced-apart along a peripheral edge of the plate; and a holder base of circular shape that has a first diameter and a center protrusion with an upwardly facing concave surface adapted for intimately engaging the convex surface on the center flexural plate so as to allow at least a 5xc2x0 tilt of the holder base from a horizontal plane, the holder base further includes at least three locating pins extending upwardly from a top surface of the holder base adapted for engaging the at least three notch openings in the center flexural plate, and means for fastening a disk onto a bottom surface of the holder base.
In the conformal disk holder for holding a rotating disk against a surface to be polished, the concave surface on the holder base allows a tilt between about 5xc2x0 and about 30xc2x0 of the holder base from a horizontal plane, and preferably a tilt between about 10xc2x0 and about 20xc2x0 of the holder base from a horizontal plane. The conformal disk may further include a CMP conditioning disk mounted to the bottom surface of the holder base. The holder base, the center flexural plate and the holder cover may be fabricated of stainless steel. The downwardly facing convex surface on the center flexural plate and the upwardly facing concave surface on the holder base may have the same curvature. The conformal disk holder may be adapted to follow the contour of a polishing pad surface in a CMP apparatus. The holder cover, the center flexural plate and the holder base are assembled together by mechanical means.
The present invention is further directed to a conformal disk holder for holding a CMP pad conditioning disk which includes a cover member of circular shape that has a first diameter, a center aperture for accessing a flexural plate member, and a means for connecting to a rotating shaft; a flexural plate member of circular shape that has a second diameter smaller than the first diameter for fitting inside a downwardly protruded edge portion on the cover member; the flexural plate member may be equipped with a center protrusion that has a downwardly facing convex surface and at least three notch openings equally spaced-apart along a peripheral edge of the plate; and a base member of circular shape that has a first diameter and a center protrusion with an upwardly facing concave surface adapted for intimately engaging the convex surface on the center flexural plate so as to allow a tilt between about 5xc2x0 and about 30xc2x0 of the base member from a horizontal plane, the base member may further include at least three locating pins extending upwardly from a top surface of the base member adapted for engaging the at least three notch openings in the flexural plate member, and means for mounting a conditioning disk onto a bottom surface of the base member.
In the conformal disk holder for holding a CMP pad conditioning disk, the flexural plate member may be equipped with a center portion that has a downwardly facing concave surface, while the base member may have a center protrusion with an upwardly facing convex surface adapted for intimately engaging the concave surface on the center flexural plate. The conformal disk holder may further include a CMP conditioning disk mounted to the bottom surface of the base member. The concave surface of the base member allows a tilt preferably between about 10xc2x0 and about 20xc2x0 of the holder base from a horizontal plane. The cover member, the flexural plate member and the base member may be fabricated of stainless steel. The downwardly facing convex surface on the flexural plate member and the upwardly facing concave surface on the base member have the same curvature to allow an intimate engagement. The cover member, the flexural plate member and the base member may be assembled together by mechanical means, such as by screws or bolts.